Removing Paint from Your Historic Building
If the painted surfaces of your historic house or building have been painted many times, you may want to remove the old paint before you paint these surfaces again. As a rule of thumb, you should probably remove all the paint to the bare wood if a painted surface has more than three complete paint jobs (nine layers of paint). You should assume that your old paint contains lead, so you should never use dry scraping (hand scraping without first moistening the surface) or power sanding to remove it. These paint removal techniques will create a lead dust hazard. Instead, you should follow some special safety procedures to manage the lead paint in your house or building.
You can choose from several different tools and devices to remove your old paint.
Using a carbide scraper is one way to remove loose paint. Source: Bob Yapp
Maintaining a sharp blade will help with removing loose paint. Source: Bob Yapp
Hand Scraping
Hand scrapers come in several different forms. The traditional scrapers have long handles and steel scraper blades. You must keep these steel blades sharp constantly with a metal file called a bastard file. If the blades are not sharp, they will glide over the loose paint without catching the edges.
The best hand scrapers today have carbide scraper blades instead of steel. Carbide scraper blades are extremely sharp and stay that way for a long time. The carbide blades have two sides, so when one gets dull or chipped you can reverse the blade. You can purchase carbide scrapers that hook up to a vacuum from marine supply stores. The vacuum hose attaches to the end of the hollow handle. These devices work well and will help you minimize paint dust. When your carbide scraper blades do get dull, you can have them re-sharpened one time at any sharpening shop that does circular saw blades. Carbide scraper blades are not inexpensive, so it makes sense to have them sharpened as needed instead of replacing them.
TIP: Before you hand scrape old paint, fill a spray bottle with water and lightly mist the painted surface. The water will keep the paint dust contained so you can vacuum and dispose of it.
Mechanical Paint Removal
Using a paint grinder with an attached hose is one way to remove paint while also capturing dust and paint particles. Source: Bob Yapp
Mechanical paint removal devices are grinders that hook up to a vacuum. These devices are designed to remove all the paint from the face of a clapboard, wood shingle or flat casing trim in one motion. All the paint debris is sucked into the vacuum. These devices remove paint very quickly and have virtually no paint dust issues. They are also approved by the Environmental Protection Agency (EPA) for safe lead paint removal.
High-Heat Paint Removal
Heat has been used to remove paint for a long time, but you would be wise to avoid using any high-heat paint removal devices. The earliest devices were basically open-flame torches. Many historic houses and buildings have burned to the ground due to the use of open-flame torches and high-heat devices for paint removal.
Heat guns are a prescription for disaster. You should never use a heat gun to remove paint in your house or building. The flash point or temperature at which wood will burst into flames is 572 degrees Fahrenheit. The average high temperature in a heat gun is 1,000 to 1,200 degrees — double the flash point temperature of wood. Using a heat gun on lead paint will create an even more significant hazard, because lead paint becomes a toxic vapor when heated above 650 degrees Fahrenheit.
Infrared Paint Removal
Infrared paint removal devices are safe and approved by the EPA for the safe removal of lead paint.
Infrared devices will not heat the wood over 560 degrees Fahrenheit when used according to the manufacturer's recommendations. This means that the wood will not catch on fire and the lead paint will not vaporize into a toxic gas. These devices remove paint by warming the resin in the wood. The warmed resin rises to the surface and pushes the paint out of molded edges and flat surfaces.
If you decide to use an infrared paint removal device, you should get one that is approved by the Underwriters Laboratory (UL). This approval will ensure that your device is electrically safe to use.
Chemical Paint Removal
Although chemical strippers for removing old paint have been available for a long time, strippers that are both safe and effective are a fairly recent invention. Until the 1990s, liquid chemical strippers typically contained a highly toxic chemical called methylene chloride. These strippers are still available today. In the refinishing business, chemical strippers are rated based on how "hot," or chemically reactive, they are. The hottest strippers remove paint very fast, and all contain methylene chloride. These strippers are so hot they can bubble up old paint so it can be removed within 10 to 15 minutes of application. However, strippers with methylene chloride can burn your skin and eyes, catch on fire, cause cancer and ruin historic wood surfaces.
Trees produce two types of wood: spring/summer wood and winter wood. You can see these two types of wood as rings on a tree stump or the end of a wood board. Spring and summer wood is the lighter and softer grain between the darker and harder winter grain. Strippers that contain methylene chloride actually burn out and erode the softer spring and summer wood grain, ruin glue joints and cause excessive shrinkage at the end of boards.
Many new citrus- and soybean-based liquid chemical strippers are now available. These new strippers have no methylene chloride, are non-flammable and have virtually no odor or volatile organic compounds (VOCs). Many are biodegradable and more environmentally sound than the old-style strippers. They are safer for you to use and will not harm historic wood. These new strippers are thick enough to hang onto vertical surfaces and hot enough to work just as well as the toxic strippers. The current generation of environmentally sound strippers can strip multiple layers of paint in about an hour. You can even recycle many of the new strippers for use on your next project.
TIP: Whenever you use a chemical paint removal device, protect your skin and eyes and follow the manufacturer's instructions for use.
The information presented here is not intended to provide comprehensive technical advice or instructions on solving historic preservation issues. Any information contained or referenced is meant to provide a basic understanding of historic preservation practices. Read full disclaimer.